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The Eighth Asia-Pacific Conference on Wind Engineering,December 10–14, 2013, Chennai, India

WAY TO INCREASE THE ROTATION EFFICIENCY OF THE WINDTURBINE USING TURBULATORS

G. Sivaraj1, K.M. Parammasivam2, M.Gokulraj3

1Assistant Professor of Aeronautical Engineering, Bannari Amman Institute of Technology, Sathyamangalam,

Tamilnadu, India, [email protected] 2 Associate Professor of Aerospace Engineering, Madras Institute of Technology Chennai, Tamilnadu, India,

[email protected] 3 Research Scholar of Aeronautical Engineering, Bannari Amman Institute of Technology, Sathyamangalam,

Tamilnadu, India, [email protected] ABSTRACT To increase the efficiency of wind turbines, rotor paining principle is very important for wind turbines with horizontal axis. It is not possible to expect the maximum efficiency from a wind turbine that is installed without doing the optimization processes. At this point, rotor blades aerodynamic features are very important. It is necessary to put forward the power value that can be obtained from rotor blades, real rotor blades have to be produced. In this paper, to increase the rotation efficiency of wind turbine blades using boundary layer blowing principle. In order to increase the use of wind energy, it is important to develop Wind turbine rotor models with high rotation rates and power coefficients. Therefore injecting a high velocity air mass into the air stream essentially tangent to the wall surface of the airfoil reverses the boundary layer friction Deceleration thus the boundary layer separation is delayed. Keywords: High rotation rate, Power coefficient, Boundary layer separation, Wind turbine blade

Introduction

Electricity is important factor in day to day life. The electrical energy was produced in many ways like nuclear power plant, thermal power plant, wind mill, etc. The nuclear power plant was very dangerous to the environment. The thermal power plant was used in coal, gas and liquid based fuel and diesel based fuel. These are the non-renewable energy source and also it increases the carbon dioxide (CO2) content of the air. It also pollutes the natural system and creates threads in future generation. Wind energy is renewable energy and it also the eco-friendly. In line with advancing technology, manufacturing costs are expected to fall below the current level. In India, the total electricity for year 2012 is 853.3 billion kWh and that level is one and half times higher than that of year 2002. The installed capacity of wind power in India was 19564.95 MW at January 2013, mainly spread across Tamil Nadu (7154 MW). Turkey also needs to increase the use of wind energy in order to raise its electricity production capacity to 60GW for year 2010. Like Turkey some countries have clean energy resource carrying no fossil based energy reserves. However, fossil energy resources such as carbon dioxide pollute the world and they are a threat to future generations. Therefore, utilizing wind energy potential is crucial in global world context.

Wind turbines are systems that harness the kinetic energy of the wind for useful

power. Wind flows over the rotor of a wind turbine, causing it to rotate on a shaft. The resulting shaft power can be used for mechanical work, like pumping water, or to turn a generator to produce electrical power.

Proc. of the 8th Asia-Pacific Conference on Wind Engineering – Nagesh R. Iyer, Prem Krishna, S. Selvi Rajan and P. Harikrishna (eds)Copyright c© 2013 APCWE-VIII. All rights reserved. Published by Research Publishing, Singapore. ISBN: 978-981-07-8011-1doi:10.3850/978-981-07-8012-8 074 1159

Proc. of the 8th Asia-Pacific Conference on Wind Engineering (APCWE-VIII)

Base bleed Base bleed is a system used on some artillery shells to increase their range, typically

by about 30%. Most of the drag on an artillery shell comes from the nose of the shell, as it pushes the air out of its way at supersonic speeds. Shaping the shell properly can reduce this greatly. Base bleed is one way to reduce this drag without extending the base of the shell. Instead, a small ring of metal extends just past the base, and the area in the rear of the shell is filled with a small gas generator.

Base bleed attachment

When placed on a blade, the center of the base bleed should be 8% - 12% after of the leading edge. For most installations a placement of 10% is deal. The length is measured along the “chord” and should not be measured along the curved portion. Specifications of base bleed are

1. From 140 mm—10 hole in diameter of 1mm 2. Inlet hole: stagnation point 3. Outlet hole: 10 % from leading edge (must be tangential)

Figure 1 a. blade with base bleed

Figure 1 b. blade with interior view of base bleed

Computational study

There are many CFD packages available in the market today. Autodesk CFD

simulator packages improve the capability of analyzing a flow and meshing the element respectively. Autodesk CFD simulator is one of the popular flow analysis packages in use today. The analysis of blade aerodynamics can present a significant challenge, requiring the simulation of many different configurations and positions of both wing and base bleed

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attachment. Wind tunnel analysis with a rolling hub is often impractical. The deployment of CFD Autodesk CFD simulator within the design process, however, enables such studies to be carried out with relative case.

Geometry Nomenclature

The blade has a length (x L), a depth (y L), and a height (z L).The blade length is aligned with the x axis, the depth with the y axis, and the height with the z axis. The flow is assumed to be symmetric about a plane that bisects the blade in the y-direction and therefore only half the blade is modeled. One corner of the blade is assumed to lie at the origin.

Meshing

An inflated boundary of prismatic elements was used near the blade surface to improve spatial resolution and gain a better understanding of boundary layer phenomena. An unstructured mesh with polyhedral elements was used for volume meshing. Simulations were carried out with the turbulence model, coupled with a blend factor of 0.5 for the advection scheme.

Analysis of wind turbine blades using Autodesk CFD simulator

Figure 2. Analysis of NACA 65410 without base bleed

Figure 3. Boundary layer separation

The Figure 3 shows the Computational analysis NACA 65410 airfoil with base bleed.

Flow increased blowing also and makes the boundary layer thinner, which in turn reduces the critical height of roughness that will cause transition.

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Figure 4. The base bleed attachment

The figure 4 show the base bleed placed on blade, the center of the base bleed should

be 10 percentages after of the leading edge. If blowing is applied through discrete holes or base bleed and is not distributed over the area, increased blowing velocities may cause the holes or base bleed to become critical themselves and act as sources for disturbances.

Experimental study

The wind tunnel model allows engineers to inexpensive tweak design for aerodynamic

performance without building numerous fully – functional prototype. The wind tunnel will serve as an educational and research tool to analysis the flow principle .It gives reliable information based on the real fluid flow which support theoretical calculation and typically used in aerodynamic research to analysis the behavior of the flow under varying condition, both within channel and over solid surfaces.

The model was designed as per the literature survey taken from journal. Then the results are compared with the literature survey. The dimensions are taken from the NTK/41 wind turbine.

Figure 5. The NACA 65410 with base bleed testing in wind tunnel

Result &Analysis

Blade model is “wall” with “blade” (in the field “Zone Name”).We considers our

model as a wind-tunnel model. So the blade is a stationary wall, the viscosity makes the air stick at the blade coachwork, so no slip the coachwork is very smooth, so a roughness of zero. Ceiling of the wind-tunnel and Side wall of the wind-tunnel are specified shear for this will

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allow the air to slip on the ceiling wall. This is not realistic, but so, we can use a very coarse mesh without boundary layer problems. Velocity is 6 m·s-1 in the Speed field. Correspond to 90km/h. and 0.05m in the “Roughness Height” field.

Table: 1 show the computation test result at velocity of 6 m/s

S.No Airfoil (NACA 65410) Achieved Velocity (m/s) Torque (N-m)

1 Wind turbine blade Without

Base bleed 7.53 0.03655

2 Wind turbine blade With base

bleed 8.01 0.171856

Figure 6. The comparisons of inlet velocity vs. outlet velocity

For comparison a rectangular modification of the original blade was designed with the

same platform area as the blades with base bleed. This modification does produce more power compared to the original blade but not as much as the cambered and twisted blade. All four upwind pointing base bleed do result in lower thrust compared the rectangular blade, while the upwind pointing base bleed results in comparable or even higher thrust.

Figure 7. The comparisons of inlet velocity vs. torque

The Figure 7 shows the base bleed system of an blades plays a crucial role in the

torque and lift coefficient. Without high-lift devices, the maximum lift coefficient, attainable by a high-aspect-ratio wing is about five times the incidence (in radians) at incidences up to stall.

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Figure 8. The comparisons of inlet velocity vs. lift coefficient

The Figure 8 determine the maximum lift coefficient as accurately as possible, since this lift coefficient corresponds to the stall speed, which is the minimum speed at which controllable speed can be maintained.

Figure 9. The comparisons of inlet velocity vs. drag coefficient

The Figure 9 determines further increase in angle of incidence will increase flow

separation on the wing upper surface, and the increased flow separation results in a loss in lift and a large increase in drag.

Figure 10. The comparisons of Inlet velocity vs. experimental model lift coefficient

Figure 11. The comparisons of Inlet velocity vs. experimental model drag coefficient

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There is no doubt that adding a base bleed to the existing blade can change the downwash distribution leading to increased produced power, but a load analysis must be made whether the additional thrust can be afforded.

Conclusions

Finally, the effect of pointing the base bleed towards the blowing side was

investigated. Based on the above mentioned results the twist distribution form base bleed was used and resulted in a slightly improved blade compared to blade with base bleed. But still there is the issue of tower clearance. Based on the present investigation it is seen that base bleed has the best overall power performance of the upwind pointing base bleed, but the increase in power of around 1.3% for wind speeds larger than 6 m/s is relatively low and must be compared to the increase in thrust of around 1.6%. But pointing the base bleed downstream seems to increase the power production even further. The effect of sweep and cant angles is not accounted for in the present investigation and could improve the performance of the base bleed even more. References

Manwell J. F. et.a. (2002), Wind Energy Explained, John Wiley & Sons Ltd., England.

Scheck, S. (2002), HAWT Aerodynamics and Models from Wind Tunnel Measurements, NREL, Colorado.

Glauert, H. (1959), The Elements of Aerofoil and Airscrew Theory, University Press, Cambrige.

Bertin, J. J. and Smith, M. L. (1998). Aerodynamics for Engineers, ThirdEdition, Prentice Hall, New Jersey.

Katz J, Plotkin J. (1991), Low Speed Aerodynamics�, McGraw- Hill Inc., New York.

Jureczko.M, Pawlak.M, Mezyk.A. (2005), Optimization of wind turbine blades, journal of materials processing technology ,167.

Sohn.Y.U, Chun.H, Kim.Y.C, Chung.C.W, Kim.Y.H, Han.K.S. (2003), Blade design of a 750Kw direct- drive wind turbine generator system.

Kong C, Kim H, Kim J. (2000), A study on structural and aerodynamic design of composite blade for large scale HAWT system, Final report, Hankuk Fiber Ltd.

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